Field of the Invention
The present invention relates to a work vehicle and a method for controlling the work vehicle.
Background Information
A work vehicle provided with a power transmission device (referred to hereinbelow as a “torque converter-type transmission”) having a torque converter and a multi-stage speed change gear is well known as a work vehicle, such as a wheel loader. However, recently electric-mechanical transmissions (EMT) have become known as power transmission devices in place of torque converter-type transmissions. As disclosed in Japanese Laid-open Patent 2006-329244, an EMT has a gear mechanism and a motor connected to a rotating element of the gear mechanism, and a portion of the driving power from the engine is converted to hydraulic pressure and transmitted to a travel device, and the remaining portion of the driving power is mechanically transmitted to the travel device.
The EMT is provided with a planetary gear mechanism and an electric motor, for example, to allow continuous speed variation. The first element among the three elements of a sun gear, a carrier, and a ring gear of the planetary gear mechanism is coupled to an input shaft, and the second element is coupled to an output shaft. The third element is coupled to the electric motor. The electric motor functions as either a motor or a generator in response to the travel state of the work vehicle. The EMT is configured to enable stepless changing of the rotation speed of the output shaft by changing the rotation speed of the electric motor.